The present invention relates to a magnetic head for recording and reading data on and from a magnetic medium, and a method for production thereof.
In a hard disk drive, data is recorded and read on and from a recording medium using a magnetic head. To increase the recording capacity per unit area of a magnetic disk, it is necessary to increase the areal density. In the current longitudinal recording method, however, when the bit length of data to be recorded is small, the areal density cannot be increased due to thermal fluctuations of medium magnetization. A solution to the problem is to adopt perpendicular magnetic recording in which magnetic signals are recorded in a direction perpendicular to a medium. Where the perpendicular magnetic recording method is used, too, such heads as a giant magneto-resistive head (GMR head), a tunneling magneto-resistive head (TMR head) having a larger reproduction output than the GMR head, and a current perpendicular to the plane type GMR head (CPP-GMR head) for passing an electric current perpendicularly to a film surface can be used for reproduction.
For recording, on the other hand, it is necessary to use a single-pole head. For perpendicular recording, as well, to increase the areal density, it is necessary to increase the track density and the linear density. To increase the linear density, it is necessary to increase the magnetic field gradient of the write head. One way to increase the magnetic field gradient is to use a two-layer recording medium having a soft under layer. To achieve a high recording density exceeding 200 Gb/in2, however, a high track density (TPI: tracks per inch) and a high linear density (BPI: bits per inch) are required. To improve the BPI value, it is necessary to increase the magnetic field gradient of the write head and the resolution of the read head. To improve the TPI value, it is necessary to reduce the track width of the head. As the track width of the head is made smaller, however, a spread of writing locations, that is, a phenomenon in which an effective track with a width larger than the actual track width (physical track width) is written on a medium has become noticeable (see FIG. 7). As a way to inhibit the spread of writing locations, it has been proposed to dispose a side shield in the vicinity of a main pole. Perpendicular magnetic recording heads provided with a side shield are disclosed in US2002/0176214A1 and JP-A No. 127480/2004.
The technical disclosures referred to by the inventor of the present invention regarding a main pole include IEEE Transactions on Magnetics, vol. 40, pp. 2329-2331 (2004) and The Journal of The Magnetics Society of Japan, Vol. 28, pp. 869-872 (2004). JP-B No. 3593312 and JP-A No. 242608/2003 include disclosures regarding the shape of a main pole. JP-B No. 3593312 discloses an example of a main pole whose width along the cross track direction increases toward its trailing edge as a measure against problems related with a skew angle. JP-A No. 242608/2003 discloses a configuration in which a main pole is divided into first and second edge portions.